Preliminary behavioral and physiological data suggest the presence of a substantial degree of within-species variation in visual capacity among squirrel monkeys (Saimiri sciureus). Thus far the variation appears to be linked to gender. Since such a variation could provide a very powerful situation in which to examine several aspects of visual physiology and behavior, as well as correlations between these two, a research program is proposed to confirm and extend this preliminary finding. To this end, psychophysical measurements of spectral sensitivity and color vision will be made for a reasonable sample of squirrel monkeys. Concurrently, electrophysiological studies involving a single-cell recording are planned which should provide information on the visual system mechanisms accounting for these variations in visual capacity. Finally, a behavioral experiment on squirrel monkeys is proposed that involves an attempt to gain information as to the significance for normal behavior of this within-species variation in visual capacity.